Technical Abstract:
Vigilant survey and eradication efforts for CTV are critical to protect citrus from infection and spread of severe CTV strains. Two notable CTV isolates were detected by the Central California Tristeza Eradication Agency (CCTEA), Tulare, CA in 1994 and 2000. The isolates, identified as Rocky Hill (RH) and Dekopon (Dk) were positive with monoclonal antibody (MAb) MCA13 and produced severe reactions in CCTEA biocharacterization tests. In 2005-2006, new investigations were conducted to compare these isolates with local ones. Aphis gossypii transmission (AT) efficiency was 74 and 23% for RH and Dk, respectively. All RH isolates including the AT sub-isolates were negative with the MAb 3E10; whereas one Dk source was positive and the other negative. Most of the Dk AT sub-isolates were negative suggesting that a mixture of strains were present. This was confirmed by SSCP profiles, nucleotide sequence, and symptoms in indicator plants. RH was a strong SY isolate and had a non-standard VT genotype. The Dk sources, in contrast, contained VT-, T3- and T30-like genotypes. Sequences from the different Dk AT sub-isolates indicated that the T3 genotype component was predominantly transmitted by aphids. In general the Dk AT sub-isolates were more severe compared to the parent isolate suggesting that Dk symptom expression was ameliorated by the mixture. Despite these differences, both RH and Dk isolates were designated as stem pitting strains with distinct genotypes and severe host reactions compared to those of local isolates.